Plants and factories utilize process control devices to control the flow of fluids in processes, wherein “fluids” may include liquids, gases, or any mixture that can flow through a pipe. Manufacturing processes that create consumer articles or goods such as fuel, food, and clothes require control valves to control and regulate fluid flow. Even a medium sized factory may utilize hundreds of control valves to control a process. Control valves have been utilized for over a century, during which time valve designers have continuously improved the operational performance of control valves.
When designing a process, the designer is faced with many design requirements and design constraints. For example, some process control applications require a valve to enable flow in two directions, which are often called bi-directional flow valves. Another example of a design constraint includes the pressure at which the fluid will be operating within the process. For example, some processes operate at relatively low pressures, e.g., less than approximately 10,000 pounds per square inch gauge sig), while other processes may operate at relatively high pressures, e.g., greater than 10,000 psig, and up to approximately 20,000 psig.
In certain circumstances, a 2-way or bi-directional valve may not be sufficient to achieve the desired functionality for a selected part of the system. Accordingly, designers wishing to equip a process system with a 3-way functionality may opt to use two separate two-way or bi-directional valves plumbed together in the same system.